1. Field of the Invention
The present invention relates to a water-cooled engine comprising: a cylinder having an axis extending generally horizontally; a piston slidably received in the cylinder to define a portion of a combustion chamber; a water jacket formed around the combustion chamber and having a cooling water outlet in its upper portion; and a water passage through which cooling water which has cooled a higher-temperature portion of the engine outside the water jacket is supplied to the water jacket.
2. Description of the Related Art
In general, a water-cooled engine is used as a vertical engine for an outboard engine system. In this type of the water-cooled engine, if a cylinder block and a cylinder head are equally cooled by cooling water, when the cylinder head of a relatively large heat release is cooled to an appropriate temperature, the cylinder block of a relatively small heat release value tends to be overcooled. Japanese Patent Application Laid-open No. 61-167111 discloses a cooling structure for an outboard engine system for cooling both a cylinder head and a cylinder block to an appropriate temperature, in order to overcome the above-described problem.
In each of embodiments and modifications (see FIG. 2, FIG. 2a to FIG. 2c, FIG. 3, FIG. 3a and FIG. 3b) described in this Japanese Patent Application Laid-open No. 61-167111, cooling water of a lower temperature from a cooling water pump is supplied to a water jacket in the cylinder head, and the cooling water consequently having a raised temperature is supplied to a water jacket in the cylinder block, thereby preventing the overcooling of the cylinder block while sufficiently cooling the cylinder head.
When cooling water is supplied to a water jacket having a cooling water outlet formed in its upper portion, if a cooling water inlet for supplying the cooling water to the water jacket is not disposed at an appropriate position, the cooling water flows downwards in a portion of the water jacket surrounding opposite left and right sides of a cylinder. Therefore, there is a possibility that the flow rate of the cooling water in various portions of the water jacket becomes uneven, resulting in a degraded cooling effect.